1. Field of the Invention
The invention generally relates to compound semiconductors. In particular, the invention relates to the protection of circuits from undesired transient voltage spikes such as those from electrostatic discharge (ESD).
2. Description of the Related Art
An undesired voltage transient on a data line can damage an electronic circuit. As technology progresses and device geometries continue to shrink, devices become ever more sensitive to voltage transients. One example of a source of an undesired voltage transient is electrostatic discharge (ESD).
Steering diodes and transient voltage suppressors have been applied to data lines in conventional circuits implemented in silicon. Where such steering diodes and/or transient voltage suppressors are fabricated from silicon on a monolithic chip, pnpn or npnp thyristor latchup can occur, which can also damage the electronic circuit. Although incorporating discrete diodes and transient voltage suppressors on a monolithic chip is possible, such incorporation techniques can involve relatively expensive double-sided processing techniques and alignment methods, which are complex, expensive, and not standard tools in the processing of silicon. Silicon has other disadvantages, such as relatively low speed and relatively low isolation between devices. The relatively low isolation between devices gives rise to relatively high leakage currents and can rapidly drain the batteries of battery-powered circuits.
Faster devices, such as heterojunction bipolar transistors (HBTs) and monolithic microwave integrated circuits (MMICs), using Group III-V compound semiconductors such as gallium arsenide (GaAs), indium phosphide (InP), and the like, are preferred in certain relatively high-speed applications, such as in relatively high-speed digital circuits and in relatively high-frequency wireless circuits. Such circuits are also sensitive to undesired voltage transients. In conventional compound semiconductor circuits, a transient voltage protection circuit is fabricated from discrete components and coupled to a monolithic compound semiconductor circuit through bond wires and die attach. This results in a relatively low assembly yield and poor performance. For example, the bond wires can exhibit relatively significant inductance, which can decrease protection from relatively fast transients. In addition, relatively high parasitic capacitance from the wire-bonded discrete components renders such transient voltage protection circuits relatively ill suited to high-speed circuits such as microwave circuits.
What is needed is a transient voltage protection circuit that is monolithically integrated in a compound semiconductor circuit to protect the sensitive devices from undesired voltage transients.